1. Field of the Invention
The present invention relates to a method of acquiring an offset deflection amount for a shaped beam and a lithography apparatus, for example, a method of acquiring an amount of swing-back to offset a displacement caused by a difference between shaping positions on an aperture plate in an electron beam shaped by first and second aperture plates and an apparatus therefor.
2. Related Art
A lithography technique which leads to development of miniaturizing a semiconductor device is only a very important process for exclusively generating a pattern in semiconduct or manufacturing processes. In recent years, with an increase in integration density of an LSI, a circuit line width required for a semiconductor device is getting smaller year by year. In order to form a desired circuit pattern on such a semiconductor device, a high-precision original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam lithography technique essentially has an excellent resolution, and is used in production of high-precision original patterns.
FIG. 14 is a conceptual diagram for explaining an operation of a variable-shaped electron beam lithography apparatus.
The variable-shaped electron beam (EB: Electron Beam) lithography apparatus operates as described below. In a first aperture plate 410, a quadrangular, for example, rectangular opening 411 to shape an electron beam 330 is formed. In a second aperture plate 420, a variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape is formed. The electron beam 330 irradiated from the charged particle source 430 and having passed through the opening 411 of the first aperture plate 410 is deflected by a deflector, passes through a part of the variable-shaped opening 421 of the second aperture plate 420, and is irradiated on a target object 340 placed on a stage continuously moving in one predetermined direction (for example, X direction). More specifically, a quadrangular shape which can pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a lithography region on the target object 340 placed on the stage continuously moving in the X direction (see Published Unexamined Japanese Patent Application No. 06-124883 (JP-A-06-124883), for example). The scheme for causing a beam to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 to form an arbitrary shape is called a variable-shaping scheme.
In the variable-shaped lithography apparatus, as described above, positions where a beam is caused to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 are changed to shape beams for writing figures of different types and different sizes. For this reason, positions where a beam is formed on the second aperture plate are different depending on figure types. For this reason, when shaped beams are deflected by the same amount of deflection with respect to all figures and irradiated on a target object, irradiation positions are misaligned by an amount of misalignment caused by a difference between positions where the beams are shaped. Therefore, an offset deflection amount (amount of swing-back deflection) must be set to each of figure types such that fixed points serving as reference positions of the figures are matched with each other.
In this case, a method for correcting misalignment is disclosed in a document (see the JP-A-06-124883, for example). The method includes: creating an optimizing template by convolution of aperture design data and a noise filter, detecting an amount of misalignment of a beam position at a peak position of a correlation function calculated by the optimizing template and a two-dimensional intensity distribution of a beam obtained by scanning the beam over a mark, and correcting the misalignment by a swing-back voltage at which the amount of misalignment is eliminated. However, because of a fine pattern and an increased in integration density of a pattern, sufficient precision cannot be easily obtained by the method. Also, a method of calculating amounts of swing-back deflection for different types of figures shaped by aperture plates is not established yet.
As described above, a method of calculating amounts of swing-back deflection for different types of figures shaped by the first and second aperture plates with high precision is not established yet.